In third conditional sentences, if the conditional clause precedes the independent clause, should a comma precede the independent clause?

(conditional clause with past perfect + comma + independent clause containing modal auxiliary + have + past participle)

I learned this rule many years ago when I was a high school student, but I noticed there are some people who no longer use a comma in third conditional sentences. There are a few answers about third conditional sentences on this website, but they contain extra variables. The following sentence is an example of a third conditional sentence with a comma.

If this area had been blank, it would have been intentional.

The next sentence is without a comma.

If this area had been blank it would have been intentional.

Which one is correct?